Phased-Array Antenna Precision Self-Calibration

ABSTRACT

Radio Frequency (RF) circuit (amplifiers, mixer, etc.) design with RFIC, e.g., implemented in CMOS, CaAs, SiGe, or other silicon processes, suffers performance variations (gain phase, frequency, bandwidth, nonlinearity) due to wafer process variations, temperature changes, and supply voltage changes, and random variations. In this invention, methods are proposed to precisely calibrate the bias current of all active devices in the system, and to precisely calibrate the gain of individual path leading to each amplifiers such that the same Pout is achieved for all antenna elements in the system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 from U.S.Provisional Application No. 63/246,221, entitled “Phase-Array AntennaPrecision Self-Calibration,” filed on Sep. 20, 2021, the subject matterof which is incorporated herein by reference.

TECHNICAL FIELD

The disclosed embodiments relate generally to phased-array antenna, and,more particularly, to method of self-calibration for phased-arrayantenna.

BACKGROUND

In antenna theory, a phased antenna array usually means an array ofantennas that creates a beam of radio waves can be electronicallysteered to point in different directions, without moving the antennas.Beamforming is technique by which an array of antennas can be steered totransmit radio signals in a specific direction. The phase and amplitudeof each signal is added constructively and distructively in such a waythat they concentrate the energy into a narrow beam or lobe. Formultiple array antennas operate in a high-density area, each arrayantenna has its own beam to point to specific user (direction). Formultiple beam array antenna, each antenna beam points to specificdirection. The bandwidth shortage increasingly experienced by mobilecarriers has motivated the exploration of the underutilized MillimeterWave (mmWave) frequency spectrum around 24G and 300 G Hz for the nextgeneration 5G broadband cellular communication networks. To supportdirectional communications with narrow beams in mmWave networks, a 5Gbase station supports multiple beam with phased-array antennas.

In a typically phased-array antenna configuration, multiple radiofrequency integrated circuits (RFICs), e.g., beamforming RFICs, areused. Each signal path for antenna element contains fixed and variablegain RF amplifiers and phase shifters. To operate a precision phasedarray function, the amplifier gain and phase shifter going into eachantenna elements needs to be precisely controlled. However, RFamplifiers within RFIC are subject to 1) PVT variation (variations inthe wafer process, supply voltage, and temperature) – typically resultsin several dBs of variations if uncompensated; and 2) random variationsdue to transistor or passive element size variations - this requirementis usually met by limiting the smallest size of transistor, capacitor,resistor to be used within the RFIC. In order to meet the high accuracyrequirement (such as 0.375 dB) for amplitude tapering across the antennaarray, it is necessary to calibrate RFICs and RF amplifiers across theantenna array.

It is expensive and complicated to calibrate a phased-array antennasystem in an over-the-air (OTA) setup for the following reasons: 1) RFAnechoic chamber is required; 2) Far field chamber can significantlyspeed up the calibration, however, a large array will require a verylarge antenna chamber; 3) Precision measurements to determine the gainand phase of each individual signal path (corresponding to each antennaelement); 4) Large number of states need to be exercise in calibration,i.e., long calibration time, adding to the cost of the system; and 5)Adequate gain adjustment range and gain resolution need to be availablefor the adjustment and calibration. To reduce the production complexityand post production antenna calibration cost, it is desirable that RFICis self-calibrated by design for different production or calibratedduring the production process by automatic test equipment. It isdesirable to have a self-calibration system that does not require anOTA/chamber setup.

SUMMARY

Radio Frequency (RF) circuit (amplifiers, mixer, etc.) design with RFIC,e.g., implemented in CMOS, CaAs, SiGe, or other silicon processes,suffers performance variations (gain phase, frequency, bandwidth,nonlinearity) due to wafer process variations, temperature changes, andsupply voltage changes, and random variations. In a phased-arrayantenna, it is important to maintain near identical performance of eachRFIC and each signal path. A phase array antenna over-the-air testingrequires expensive antenna chamber and takes a very long time (costly).In this invention, methods are proposed to precisely calibrate the biascurrent of all active devices in the system, and to precisely calibratethe gain of individual signal path leading to each amplifiers such thatthe same Pout is achieved for all antenna elements in the system. Notethat this type of calibration involves only current measurements and notest instrument and no OTA (over-the-air) testing is used. Therefore,such calibration can be done in the filed or in the factory andsignificantly reduces the test time in the chamber for mass production.

In one embodiment, a calibration circuit powers off all active circuitsand power amplifiers on RFICs of a phased-array antenna. The calibrationcircuit powers on an active circuit of an RFIC under calibration andmonitor a current draw from the active circuit. The calibration circuitmeasures a bias current of the active circuit and adjusts the biascurrent to a predefined level during calibration. The calibrationcircuit repeats the calibration of the bias current for each activecircuit of the RFIC and for all the RFICs within the phased-arrayantenna.

In another embodiment, the calibration circuit powers off all activecircuits and power amplifiers on RFICs of a phased-array antenna andpowering on a power amplifier and a corresponding signal path leading tothe power amplifier of an RFIC under calibration. The calibrationcircuit provides an input signal having a predetermined signal level andmeasures a dynamic current of the power amplifier under calibration. Thecalibration circuit adjusts an amplifier gain and an output power of thecorresponding signal path leading to the power amplifier until achievinga desired dynamic current of the power amplifier. The calibrationcircuit repeats the calibration of the output power for each poweramplifier and the corresponding signal path of the RFIC with the sameinput signal having the pre-determined signal level and for all RFICswithin the phased-array antenna.

Other embodiments and advantages are described in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a typical transmit phased-arrayantenna configuration of a base station with self-calibration mechanismin accordance with one novel aspect.

FIG. 2 illustrates an RFIC bias generation system that generates biascurrent to be used for RF amplifier circuits.

FIG. 3 is a simplified circuit diagram of a bias generator supportingconstant gm bias to be used in radio frequency amplifiers in RFIC.

FIG. 4 illustrates one embodiment of a current measuring circuit thatcan be used for bias current calibration in phased-array antenna.

FIG. 5 is a flow chart of a procedure for self-calibrating bias currentin phased-array antenna in accordance with one novel aspect.

FIG. 6 illustrates one embodiment of a bias current self-calibrationsystem for phased-array antenna in accordance with one novel aspect.

FIG. 7 illustrates different power amplifier classes and the dynamiccurrent at proper backoff operating point of a power amplifier.

FIG. 8 is a flow chart of a procedure for self-calibrating output powerin phased-array antenna in accordance with one novel aspect.

FIG. 9 illustrates one embodiment of output power self-calibrationsystem for phased-array antenna in accordance with one novel aspect.

FIG. 10 is a flow chart of a method for self-calibrating bias currentsof active circuits on RFICs of a phased-array antenna in accordance withone novel aspect.

FIG. 11 is a flow chart of a method for self-calibrating output powersof power amplifiers on RFICs of a phased-array antenna in accordancewith one novel aspect.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 is a simplified block diagram of a typical transmit phased-arrayantenna configuration, containing of multiple RFICs distributed acrossantenna aperture, of a base station 101 with self-calibration mechanismin accordance with one novel aspect. Beamforming cellular mobilecommunication network 100 comprises a base station BS 101 and aplurality of user equipments including UE 102 and UE 103. The cellularmobile communication network uses directional communications with narrowbeams and can support multi-gigabit data rate. One example of suchcellular network is a Millimeter Wave (mmWave) network utilizing themmWave frequency spectrum. In such mmWave network, directionalcommunications are achieved via beamforming, wherein a phased antennaarray 110 having multiple antenna elements are applied with multiplesets of beamforming weights (phase shift values) to form multiple beampatterns, which are required to overcome high path loss in the mmWavenetwork and to provide mobility support for mobile terminals. Due tohigh signal loss in the antenna, package, module, and PCB substrate, itis desirable to place active circuits (power amplifier and low noiseamplifiers) in close proximity to the corresponding antenna elements, toreduce the passive loss. This results in a distributed RFIC placementacross the antenna aperture with one RFIC serving a few number ofantenna elements in its proximity. In the example of FIG. 1 , phasedantenna array 110 of BS 101 is directionally configured with a set ofcoarse TX/RX control beams (130) and a set of dedicated TX/RX data beams(140) to serve mobile stations including UE 102 and UE 103.

In the example of FIG. 1 , BS 101 comprises phased-array antennas 110coupled to a combiner splitter network 120. For multiple array antennasoperate in a high-density area, each array antenna has its own beam topoint to a specific UE (direction). In a typical phased-array antennaconfiguration, multiple radio frequency integrated circuits (RFICs),e.g., beamforming RFICs, are used. Each RFIC contains multiple signalpaths to antenna elements. Each signal path for an antenna elementcontains fixed and variable gain amplifiers and phase shifters. Tooperate a precision phased array function, the amplifier gain and phaseshifter going into each antenna elements needs to be preciselycontrolled. However, RF amplifiers within RFIC are subject to 1) PVTvariation (variations in the wafer process, supply voltage, andtemperature) – typically results in several dBs of variations ifuncompensated; and 2) random variations due to transistor or passiveelement size variations and threshold variations - this requirement isusually met by limiting the smallest size of transistor, capacitor,resistor to be used within the RFIC. In order to meet the high accuracyrequirement (such as less than half of 0.375 dB) for amplitude taperingacross the antenna array to achieve the desired sibelobe or interferencesuppression, it is necessary to calibrate the active circuit with theRFICs across the antenna array.

It is expensive and complicated to calibrate a phased-array antennasystem in an over-the-air (OTA) setup for the following reasons: 1) RFAnechoic chamber is required; 2) Far field chamber can significantlyspeed up the calibration, however, a large array will require a verylarge antenna chamber or a field test range; 3) Precision measurementsto determine the gain and phase of each individual signal path(corresponding to each antenna element) at the operating frequency (e.g.mmWave); 4) Large number of states need to be exercise in calibration,i.e., long calibration time, adding to the cost of the system; and 5)Adequate gain adjustment range and gain resolution need to be availablefor the adjustment and calibration. To reduce the production complexityand post production antenna calibration cost, it is desirable that RFICis self-compensated by design for different production or calibratedduring the production process by a simple automatic test equipment whichonly requires DC measurements. It is desirable to have aself-calibration system that does not require an OTA/chamber setup.

In accordance with one novel aspect, a procedure for phased-arrayantenna having RFIC with precision self-calibration is proposed (150).In a first novel aspect, a calibration control procedure is coupled withthe calibration circuit, which consists of a controller and a currentmeter, switches, and bias adjustment circuits, for the bias current in aphased-array antenna is proposed. The bias currents of the activecircuits within the system are self-calibrated upon power-up. At theinitial stage, all active circuits are turned off. One-by-one, theselected individual active circuit is turned on and its bias current ismeasured with a current meter within the system. Each active circuitcontains a current adjustment circuit (i.e., a current DAC“digital-to-analog converter”) for adjusting the bias current of thecircuit. The bias current of the selected active circuit can be adjustedvia changing the current DAC setting by the controller until reachingthe desired accuracy against a pre-defined level for the selected activedevice. The calibration is repeated until the bias currents of all theactive circuits within the system are calibrated. In a second novelaspect, a self-calibration procedure for the output power of each signalpath within the phased-array antenna system is proposed. The gain ofeach individual path is precisely calibrated such that the same outputpower is achieved for all power amplifiers corresponding to all antennaelements in the system.

FIG. 2 illustrates an RFIC bias generation system 200 that generatesconstant bias currents to be used for RF amplifier circuits. The RFICbias generation system 200 comprises a bandgap (BG) voltage source 201that provides a constant voltage, which is converted to a constantcurrent (called the global reference current) by V-To-I circuit 202. Theglobal reference current is then used by a global one-to-many mirroringcircuit 203 to generate many mirroring currents, e.g., 100 µPPE and 100µPE, which are used by a plurality of one-to-many mirroring circuits204, for outputting a plurality of reference currents 1, 2, ... and soon so forth. The reference currents are in turn provided to generatebias currents to be used for amplifier circuits, via the mirroring orreplica bias circuits 205. Each individual circuit has a custom designedmirroring or replica bias circuits to generate the desired bias currentin proportional to the reference currents. For example, bias current 1for active circuit 1, bias current 2 for the active circuit 2, ... andso on so forth. Ideally, each of the bias currents should have thedesired constant bias current level.

The gain of a transistor amplifier is determined by 1) Transistor sizeand the width versus length (W/L) ratio (subject to the productionvariations). Percentage of the size variation is reduced if biggertransistor size is used; and 2) The bias current which transistoramplifier is operating at. As illustrated in FIG. 2 , in order toachieve the precision bias current at the amplifiers, the RFIC typicallyimplements a bias generation system 200 which consists of 1) Bandgapreference voltage source; 2) Reference voltage to reference currentconversion; 3) One-to many reference current mirroring; and 4) Deliveryof reference currents to individual amplifiers. At each amplifier, thebias circuit utilize either a mirroring circuit or replica circuit toscale the reference current to the desired operating bias current. Oneof the major contributors to the errors in bias current mirroring orreplica circuit is the Vth threshold voltages, which can have randomvariations from transistor to transistor. Even if transistor sizeproduction variations are acceptable, variations in the Vth thresholdvoltage can affect the accuracy in the bias current.

FIG. 3 is a simplified circuit diagram of a bias generator 301supporting constant gm bias to be used in radio frequency amplifiers inRFIC. Bias generator 301 comprises a pair of transistors M1 and M2, thegate of M1 and M2 are coupled by an external resistor R_(EXT).Transistor M1 has a size of W/L, and transistor M2 has a size ofK*(W/L). As depicted in FIG. 3 , the constant G_(m) bias is determinedby R_(EXT) and the transistor size radio K only:

$g_{m}\, = {2/{\text{R}_{\text{EXT}}\mspace{6mu} \ast \mspace{6mu}\left( {1\mspace{6mu} - \mspace{6mu}{1/\left. \sqrt{}\text{K} \right.}} \right)}}\mspace{6mu}$

, wherein R_(EXT) is a precision resistor with zero temperaturecoefficient. Therefore, because the Gm and the reference voltage are PVTindependent, then the fixed current generated using these parameters isalso PVT independent and hence can be used as a master bias current fora large RFIC. In FIG. 3 , Iref1 and Iref2 are different bias currentmirrors to be used for different RF amplifiers.

Note that the size ratio K between transistor M1 and transistor M2 iscritical for obtaining the precise value of Gm. Additionally, thetransistor M1 should replicate the transistor used in the RF amplifiersto maintain good tracking of Gm. It is thus critical to use the sametype of transistor and the size. As a result, transistor M2 is formed byreplicating K identical transistors M1 having the same size of (W/L).Further, the current density of the transistors should be the same asthe current density of the RF amplifier. Therefore, while increasingtransistor size can improve the accuracy of the size ratio K, it is notdesirable to have a large sized M1 and M2 transistors in order toachieve low power consumption and smaller size of the RFIC.

As explained above, a constant Gm bias is for maintaining thetransconductance gain of the amplifier across wafer. A precision andtemperature-stable off-chip resistor for each RFIC is used as areference and the transistor size ratio is used to obtain a precisionGm. However, the accuracy is affected by the variations in thetransistor threshold voltage V_(th). In the CMOS semiconductor process,the threshold voltage V_(th) of transistor has high level of variationseven within the same wafer. The transistor threshold voltage for M1 isV_(th),₁, and the transistor threshold voltage for M2 is V_(th),₂. Thisis the dominant contributor to the error in the bias current of theamplifier generated by the mirroring circuit or replicate bias circuitfrom the reference current, as illustrated in FIG. 2 . The error in theamplifier bias current affect the performance of the amplifier, e.g.,Gm~Sqrt Root of Bias Current. Therefore, it is necessary to calibratethe error in the bias current accurately to improve amplifierperformance.

In one embodiment, PTAT (proportional to absolute temperature) currentsources are used to generate bias currents for active devices in an IC.They are also employed in-bandgap reference circuits which are commonlyused to generate temperature independent (or temperature dependent) biasvoltages and as reference in measurement systems. The bias current canincrease or decrease as a function of temperature, it compensates forthe variation in the Gm (Transconductance Gain) of the transistor tomaintain its performance over temperature.

FIG. 4 illustrates one embodiment of a current measuring circuit(current meter) 400 that can be used as a self-calibrating system forphased-array antennas. A self-calibration system self-calibrates thebias current of power amplifiers in a phased-array antenna upon powerup. The self-calibrating system consists of a uC with an analog todigital converter (ADC) which can measure the current, i.e., the voltagedrop across a precision resistor R and in addition, the uC controls thecircuits turn on and off and the setting of the corresponding biasadjustment for each circuit. The self-calibrating system has the abilityto control the bias generation with the RFIC to turn on/off of the biasof each individual circuit, and to turn on/off the main power managementsystem which supply voltage to the RFIC. A separate supply voltage forperforming calibration is provided when the main voltage supply for thesystem is turned off.

Calibration is performed one circuit at a time, i.e., the current to bemeasured is low to allow precision current (i.e., the voltage drop ofthe current across a precision resistor) measurement by the ADC(typically within the uC). Each circuit contains a current DAC whichinjects a correction current into the mirroring or replicate biascircuit for the circuit to adjust the bias circuit under the control ofthe uC. The key reason to employs a separate supply voltage forperforming calibration is to avoid this precision resistor in the pathof main power supply which can consume unnecessary power duringoperation (after calibration is complete). The RFIC can adjust the biascurrent during calibration until it reaches the pre-defined level withan acceptable tolerance.

In the example of FIG. 4 , the current measuring circuit 400 comprisesµC, ADC, iDAC, and Precision R. The µC measures current I by using ADCto measure voltage V across a precision resistor R, e.g., I=V/R. Toavoid precision resistor R dissipates power during regular operation,the main voltage supply for the system is turned off and an auxiliaryvoltage supply for calibration is switched on during measurement. The uCadjust the current Digital to analog converter (iDAC) until the desiredbias current is measured. For example, a 4 to 6-bit control signal canbe used to adjust the iDAC until achieving the desired bias current.Note that each amplifier or active circuit within the system can beturned on and off under uC control. This measurement is repeated foreach active circuit within the system while all the other circuits areturned off.

FIG. 5 is a flow chart of a procedure for self-calibrating bias currentof power amplifiers in a phased-array antenna in accordance with onenovel aspect. Step 501 is the initialization stage, where the followingactions are performed by a self-calibration system: 1) turn off allamplifier circuits; 2) turn off all regulators providing the DC supplyvoltages to all RFICs; In step 502, one by one, the self-calibrationsystem turns on the individual power amplifier and measures the biascurrent: 1) turn on the voltage supply for self-calibration, Global BiasGenerator and the bias generator associated with a selected circuit,measure the current, 2) turn on the selected active circuit, 3) monitorthe increased current draw of the selected circuit, and 4) theself-calibration system adjusts the bias current (via changing thesetting of the iDAC) of each active device until it reaches the desiredaccuracy.

FIG. 6 illustrates one embodiment of a bias current self-calibrationsystem 600 for phased-array antenna in accordance with one novel aspect.The self-calibration system 600 is similar to the current measuringcircuit 400, but is implemented with additional regulators and switchesfor calibrating circuits (system under test) that have three differentsupply voltages for operation and divided into four power supplydomains. The different supply voltages, 1 volt, 1.7 volt, and 3.3 volt,can be calibrated separately, e.g., controlled by the regulators andswitches; the four power supply domains can also be calibratedseparately to reduce power consumption, e.g., controlled by theregulators and switches, and the calibration is repeated in each powersupply domain. This allows low cost commercial off-the-shelf powersupply to be used. During calibration, all circuits are turned offexcept one circuit to be tested. For each circuit, adjust DAC bias inthe current mirror until the desired voltage drop as measured by the ADCis achieved.

Note the self-calibration is performed in foreground, meaning thephased-array antenna system is not in normal operating state. Theself-calibration can be performed at initial power-up or during thesystem idle or maintenance time. The self-calibration achieves theprecise bias current for the amplifiers, which means that preciseamplifier gain can be achieved as well. The self-calibration systemreduces cost because it does not require using OTA chamber setup.

In 3GPP or IEEE wireless systems, high order modulation scheme such asOFDM with 64 QAM, 256 QAM or 1024 QAM are used. This type of modulationrequires the power amplifier to operate at linear region to avoid highEVM (error vector magnitude). In a phased-array antenna, it is desirableto monitor the output power from the IC going into each antenna element,for the purpose of creating precise antenna pattern, and for avoidingpower amplifier nonlinearity (driving the PA at the proper backoff).Since an input signal can go through many stages of active devicesbefore reach the power amplifier, each stage of an device contributessome error in the amplifier gain. It is thus desirable to measure theoutput power and adjust the gain to maintain the signal level at theproper power amplifier operation point.

FIG. 7 illustrates different power amplifier classes and the dynamiccurrent at proper backoff operating point of a power amplifier. Notethat the average power consumption of the power amplifier (if it is notclass A amplifier) depends on its operating level (signal level). Whenthere is no input signal, there power amplifier will have quiescentcurrent. When the input signal increases, the bias current of PA alsoincreases. Dynamic current is the average operating bias currentsubtract the quiescent current. As illustrated in FIG. 7 , small signaldoes not trigger current conduction, and higher signal creates highcurrent conduction duty cycle.

The proposed invention is to implement the power detector based onmeasurement of the dynamic current of the PA at the proper backoffoperating point of the PA. In the preferred embodiment of a CMOS ClassA-B PA, it is found that back-offing about 6 or 7 dB from output powerP1dB, the dynamic current accurately reflect output power levelregardless of semiconductor process corners and temperatures.

FIG. 8 is a flow chart of a procedure for self-calibrating output powerin phased-array antenna in accordance with one novel aspect. For outputpower measurement, the same bias current measuring system as illustratedearlier is applied for measuring the dynamic current. In step 801,turned off all active circuits except for the active circuits in theselect signal paths under calibration. In step 802, input a signal ofknown signal level and measuring dynamic current of PA. Note that theinput signal is typically CW (Continuous wave) and the input signallevel is selected at the pre-defined output power level corresponding tothe most accurate dynamic current (i.e., least amount of dynamicvariations due to process, supply voltage changes. First measuring thequiescent current while input is off and then measure bias current wheninput signal is on to derive the dynamic current (i.e., the operatingbias current with input signal minus the quiescent current). In step803, adjust the amplifier gain of the selected signal path leading tothat power amplifier until desired dynamic current of the PA isachieved. Compensate error ΔG by adjusting the variable gain amplifierin each path. In step 804, repeat the same procedure to all the poweramplifiers in all the signal paths within the system until all PAsachieve the same dynamic current (Pout).

FIG. 9 illustrates one embodiment of output power self-calibrationsystem 900 for phased-array antenna in accordance with one novel aspect.The output power self-calibration system 900 is similar to the biascurrent self-calibration system 600 illustrated in FIG. 6 , and isimplemented with additional regulators and switches for calibratingcircuits (system under test) that have three different supply voltagesfor operation and divided into four power domains. The different supplyvoltages, 1 volt, 1.7 volt, and 3.3 volt, can be calibrated separately,e.g., controlled by the regulators and switches; the four power domainscan also be calibrated separately to reduce power consumption, e.g.,controlled by the regulators and switches. During calibration, allcircuits are turned off except one circuit to be tested. For eachcircuit, 1) measure the output power Pout; 2) measure the gainG=Pout/Pin; 3) compensate error ΔG by adjusting the variable gain of thepower amplifier of the selected path, until the desired dynamic currentof the power amplifier is achieved.

Whole signal chain calibration can be done by monitor the 1.7 v PAdynamic current. Because the gain/power is flatter at the centerfrequency, to minimize gain/power sensitivity to process andtemperature, all stages need to be tuned to the correct centerfrequency. Frequency tuning step need to be fine enough to limit theerror to less than ½ LSB of 0.375 dB. Calibration can be carryout byfirst fine tune the center frequency of all stages to the desirefrequency, then adjust the gain to reach the desire 1.7 v PA dynamiccurrent. To conclude, above 6dbm, the error is less than ½ LSB of 0.375dBm over process corner. The error over temperature ( 30° C. to 80° C. )is more than 1.5 LSB and come from center frequency shift due totemperature. The error may be smaller if operate at center frequency.Re-simulation over temperature at corresponding center frequencyverifies that sensitivity of temperature can be reduced to an acceptablelevel by operating only at center frequency. The calibration procedurecan be performed at different signal frequencies and the calibratedsetting can be stored in the uC which can be loaded depending on whichsignal frequency is selected.

FIG. 10 is a flow chart of a method for self-calibrating bias currentsof active circuits on RFICs of a phased-array antenna in accordance withone novel aspect. In step 1001, a calibration circuit powers off allactive circuits and power amplifiers on the RFICs. In step 1002, thecalibration circuit powers on an active circuit of an RFIC undercalibration and monitor a current draw from the active circuit. In step1003, the calibration circuit measures a bias current of the activecircuit and adjusts the bias current to a predefined level duringcalibration. In step 1004, the calibration circuit repeats thecalibration of the bias current for each active circuit of the RFIC andfor all the RFICs within the phased-array antenna.

FIG. 11 is a flow chart of a method for self-calibrating output powersof power amplifiers on RFICs of a phased-array antenna in accordancewith one novel aspect. In step 1101, the calibration circuit powers offall active circuits and power amplifiers on the RFICs and powering on apower amplifier and a corresponding signal path leading to the poweramplifier of an RFIC under calibration. In step 1102, the calibrationcircuit provides an input signal having a predetermined signal level andmeasures a dynamic current of the power amplifier under calibration. Instep 1103, the calibration circuit adjusts an amplifier gain and anoutput power of the corresponding signal path leading to the poweramplifier until achieving a desired dynamic current of the poweramplifier. In step 1104, the calibration circuit repeats the calibrationof the output power for each power amplifier and the correspondingsignal path of the RFIC with the same input signal having thepre-determined signal level and for all RFICs within the phased-arrayantenna.

Although the present invention has been described in connection withcertain specific embodiments for instructional purposes, the presentinvention is not limited thereto. Accordingly, various modifications,adaptations, and combinations of various features of the describedembodiments can be practiced without departing from the scope of theinvention as set forth in the claims.

What is claimed is:
 1. A method of self-calibration for radio frequencyintegrated circuits (RFICs) within a phased-array antenna, comprising:powering off all active circuits and power amplifiers on the RFICs;powering on an active circuit of an RFIC under calibration and monitor acurrent draw from the active circuit; measuring a bias current of theactive circuit and adjusting the bias current to a predefined levelduring calibration; repeating the calibration of the bias current foreach active circuit of the RFIC and for all the RFICs within thephased-array antenna.
 2. The method of claim 1, wherein the bias currentis measured by a µC using an analog-to-digital converter (ADC) tomeasure a voltage across a precision resistor R.
 3. The method of claim2, wherein the µC adjusts a current digital-to-analog converter (DAC)until achieving a desired bias current.
 4. The method of claim 1,wherein each active circuit within the RFIC can be turned on or offunder the µC control.
 5. The method of claim 1, wherein a main voltagesupply is turned off and an auxiliary voltage supply is turned on duringthe bias current measurement.
 6. A method of self-calibration for radiofrequency integrated circuits (RFICs) within a phased-array antenna,comprising: powering off all active circuits and power amplifiers on theRFICs and powering on a power amplifier and a corresponding signal pathleading to the power amplifier of an RFIC under calibration; inputtingan input signal having a pre-determined signal level and measuring adynamic current of the power amplifier under calibration; adjusting anamplifier gain and an output power of the corresponding signal pathleading to the power amplifier until achieving a desired dynamic currentof the power amplifier; and repeating the calibration of the outputpower for each power amplifier and the corresponding signal path of theRFIC with the same input signal having the pre-determined signal leveland for all RFICs within the phased-array antenna.
 7. The method ofclaim 6, wherein the measuring of the dynamic current of the poweramplifier involves measuring a quiescent current while the input signalis off and then measuring the bias current when the input signal is on.8. The method of claim 7, wherein the dynamic current is equal to anaverage bias current subtract the quiescent current.
 9. The method ofclaim 6, wherein the dynamic current is measured at a pre-determinedbackoff operating point of the power amplifier corresponding to highaccuracy.
 10. The method of claim 9, wherein the desired dynamic currentreflects the output power level at the predetermined backoff operatingpoint.
 11. A phased-array antenna comprising a plurality of radiofrequency integrated circuits (RFICs), wherein each RFIC comprises: aplurality of active circuits and powering power amplifiers that arepowered off initially, wherein an active circuit of an RFIC undercalibration is powered on; a measuring circuit comprising a µC thatmonitors a current draw from the active circuit, wherein the µC measuresa bias current of the active circuit and adjusts the bias current duringcalibration; and a plurality of regulators and switches that repeats thecalibration of the bias current for each active circuit of the RFIC. 12.The phased-array antenna of claim 11, wherein the µC measures the biascurrent using an analog-to-digital converter (ADC) to measure a voltageacross a precision resistor R.
 13. The phased-array antenna of claim 12,wherein the µC adjusts a current digital-to-analog converter (DAC) untilachieving a desired bias current.
 14. The phased-array antenna of claim11, wherein each active circuit within the RFIC can be turned on or offunder the µC control.
 15. The phased-array antenna of claim 11, whereina main voltage supply is turned off and an auxiliary voltage supply isturned on during the bias current measurement.
 16. The phased-arrayantenna of claim 11, wherein each RFIC further comprises: an input nodethat receives an input signal having a pre-determined signal level,wherein a dynamic current of a power amplifier of the RFIC undercalibration is measured; and an output node that outputs an output powerof a selected signal path leading to the power amplifier, wherein theoutput power is adjusted by adjusting a gain in the selected signal pathuntil a desired dynamic current is achieved, wherein the calibration ofthe output power is repeated for each power amplifier of the RFIC. 17.The phased-array antenna of claim 16, wherein the measuring of thedynamic current of the power amplifier involves measuring a quiescentcurrent while the input signal is off and then measuring the biascurrent when the input signal is on.
 18. The phased-array antenna ofclaim 17, wherein the dynamic current is equal to an average biascurrent subtract the quiescent current.
 19. The phased-array antenna ofclaim 16, wherein the dynamic current is measured at a backoff operatingpoint of the power amplifier.
 20. The phased-array antenna of claim 19,wherein the desired dynamic current reflects the output power level atthe backoff operating point.